1. Field of the Invention
The present invention relates to a stacked heat exchanger which can be used as an evaporator of an air conditioner, particularly suitable as an evaporator in automotive air conditioners, and a method of manufacturing the same.
2. Description of the Related Art
A conventional stacked heat exchanger will be described with reference to FIGS. 19 and 20. FIG. 19 is a front view of a conventional stacked heat exchanger, and FIG. 20 is an expanded cross-sectional view of its right side portion.
Referring to FIGS. 19 and 20, reference numeral 1 denotes a flat tube. It is formed of two press-formed plates 2 which are butted together. An inlet/outlet tank portion 3 is formed at one end (upper end in the figure) of the flat tube 1.
A stacked heat exchanger (evaporator) 5 is constructed by alternately putting flat tubes 1 and corrugated fins 4 together and connecting the inlet/outlet tanks 3.
The outside of the flat tube la located at each end of the heat exchanger constitutes an end plate 6, and the end plate is provided with a through hole 7 at the inlet/outlet tank portion 3. The through hole 7 at one end is connected to an inlet pipe 8 for the refrigerant, while the through hole 7 at the other end is connected to an outlet pipe 9 for the refrigerant.
The inlet and outlet pipes 8, 9 are fixed to the end plate 6 by brazing. Between the side plate 10 and the end plate 6 are provided corrugated fins 4.
The inlet/outlet tank portion 3 is partitioned into an inlet portion 11 and an outlet portion 12 in the panel width direction of the flat tube 1. When the evaporator 5 is constructed, the inlet portions 11 of the adjacent inlet/outlet tank portions, as well as the outlet portions 12 thereof, communicate with each other through communicating holes 13.
The flat tube 1 will be described with reference to FIGS. 21 and 22. FIG. 21 is a front view of a plate 2 forming the flat tube 1, and FIG. 22 is a cross-sectional view taken along the line D--D of FIG. 21.
The upper end portion of the plate 2 is provided with an expanded portion 14 for forming the inlet/outlet tank portion 3. The hollow portion of the plate 2 is divided into two chambers 16 and 17 by a partition 15 extending vertically at the center. The lower end portion of the partition 15 is cut short and does not reach the bottom of the plate 2, so that the lower end of the plate 2 can constitute a U-turn portion 18 for allowing the U-turn of refrigerant. By butting two plates 2 together, the inlet/outlet tank portion 3 is divided into the inlet portion 11 and the outlet portion 12 by the partition 15, and at the same time the flat tube is divided into the chamber 16 communicating with the inlet portion 11 and the chamber 17 communicating with the outlet portion 12. Further, the chamber 16 communicates with the chamber 17 at the U-turn portion 18. Thus, the chambers 16 and 17 and the U-turn portion 18 form a fluid passage.
In the chambers 16 and 17, many ribs protrude, so that the inside of the chambers 16 and 17 is fractionized like a maze. At the U-turn portion 18, guide ribs 20 protrude, so that the U-turn flow of refrigerant is guided from the chamber 16 to the chamber 17 by the guide ribs 20.
Next, the flow of refrigerant in the above-described evaporator 5 will be described with reference to FIG. 23. FIG. 23 shows the flow of refrigerant.
The evaporator 5 is broadly divided into three groups 21, 22, and 23. The arrangements of the inlet portion 11 and the outlet portion 12 of the groups 21 and 23 connected to the inlet pipe 8 and the outlet pipe 9, respectively, are the same, but the arrangement of the inlet portion 11 and the outlet portion 12 of the group 22 is reversed. For the inlet/outlet tank portion 3 opposing between the group 21 and the group 22 and between the group 22 and the group 23, the outlet portion 12 of the group 21 communicates with the inlet portion 11 of the group 22, and the outlet portion 12 of the group 22 communicates with the inlet portion 11 of the group 23. The inlet portion 11 of the group 21 is connected to the inlet pipe 8 through the through hole 7 of the end plate 6, while the outlet portion 12 of the group 23 is connected to the outlet pipe 9 through the through hole 7.
A refrigerant 31 introduced into the evaporator 5 through the inlet pipe 8 is sent from the inlet portion 11 of the group 21 to the U-turn portion 18 through the chamber 16, makes a U-turn, and is sent to the outlet portion 12 through the chamber 17. The refrigerant 31 which has been sent to the output portion 12 of the group 21 is sent to the inlet portion of the group 22, and then is sent to the group 23 after flowing in the group 22 in the same way as in the group 21. Finally, the refrigerant 31 is discharged from the outlet pipe 9 after flowing in the fluid passage (chambers 16 and 17, U-turn portion 18) of the group 23.
In this process, air 32 is sent to between the corrugated fins 4, so that the air 32 is cooled by using the latent heat of evaporation of the refrigerant 31.
For the above-described evaporator 5, the corrugated fins 4 are disposed between the plates 2 and stacked. The stacked corrugated fins are joined integrally by brazing.
In the above-described conventional evaporator 5, many ribs 19 are installed in the chambers 16 and 17 on the inside of the plate 2 of the flat tube 1 to increase the heat transfer area for the refrigerant. However, the refrigerant sometimes does not flow smoothly because the flow paths are like a maze. Moreover, at the U-turn portion 18, though the U-turn of the refrigerant is guided by the guide ribs 20, the refrigerant is separated into two phases of gas and liquid by centrifugal force, so that the gas and liquid cannot be distributed uniformly in the flow direction, decreasing the efficiency of heat exchange.
Also, the conventional evaporator 5 is undesirable because the entirety of the evaporator is greatly deformed under repeated pressurization when only ribs 19 are installed, as seen from the deformation mode shown in FIG. 14. Therefore, there has been anxiety in terms of strength under pressure.
The evaporator 5 has so far been manufactured so that the corrugated fins 4 are disposed between the plates 2, stacked and brazed. In this case, a high accuracy of positioning of the corrugated fins 4 with respect to the plate 2 can be maintained. However, it has been difficult to maintain a high joining accuracy of the flat tube composed of two joined plates 2, which makes the reliability of the flat tube 1 poor.